Contact for electrical apparatus



Jan. 25, 1938.

R. WILKINS CONTACT FOR ELECTRICAL APPARATUS Filed Sept. 8, 195a Patented Jan. 25, 1938 2,106,332 a n o i CONTACT FOR ELECTRICAL APPARATUS. v a Roy Wilkins, San Francisco, Calif., assign r to K. P. Calif.

F, Electric Company, San Francisco,

Application September 8, 1936, Serial No. 99,744

7 Claims.

The present invention relates'to an electrical apparatus, and more particularly to an improved contact surface and method of forming same upon the engaging parts of copper current conducting members of electrical apparatus and circuits.

An object of the invention is to provide animproved contact surface forthe engaging parts of current carrying conductors which will have im- 0 proved non-heating and current carrying characteristics.

Another object of the invention is to provide a novel form of contacting surface for the engaging parts of current conducting members,

which is of a non-insulating film forming character.

Another object of the invention is to provide a new and novel method of applying silver and like metals to the contact forming surfaces of electrical switch contacts.

It is well known that under normally elevated temperatures copper tends to oxidize and thus form an insulating film upon the surface thereof. This oxidation upon the contacting surfaces of copper conductors also causes increased heating at the contact when heavy currents are transmitted therethrough, and this heating in turn accelerates the process of oxidation and may eventually result in a temperature sufficiently high to anneal the copper parts, and in extreme cases pit and otherwise physically damage the contacting surfaces. To overcome this disadvantage many manufacturers of switches have res sorted to a plating of the cooperating contact surfaces of the switch with silver, both by the electroplating method and in accordance with the so-called fSchoup spray process; while I others have resorted to the brazing of a sheet of silver upon the cooperating contact forming surfaces of .the switch contacts. -Whi1e these courses of procedure have been found to overcome the objections due to oxidation of the copper, assuggested above, resort to these methods -'comp1icates the, manufacturing operations and greatlyincreases the cost of theapparatus. It

is therefore a further object of the presentin I vention to provideal new and novel method for applying a non-oxidizing-contact surface to the cooperating surfaces of the current conducting memberswhich will overcome theabove difficulties, and at the same time provide a simple,

practical and less expensive-construction. H

scription thereof, taken in connection with the accompanying drawing, proceeds,

In the drawing, whereinlthere is shownby way of illustration and not of limitation, fpreferred embodiments of the invention:

Figure 1 is a fragmentary side view" showing the cooperating contact forming members'oi va high-voltage d'isconnecting s'witch, j

Figure 2 is a view showingthe position of the; blade and the cooperating'contact clips -of,;the 10 switch of Figure 1, whenthe switch blade is in its circuit closed position", a r V Figure 3 is aperspective view's howing] thedetails of construction of the switchclip illustrated in Figures 1 and 2 of; the drawing, o

Figure 4 is a perspective view showing the ,details of .the switch blade illustrated: inFigures 1 and'2of the drawing, 'p

Figure 5 is, a perspective view showing the manner of applying the invention to a switch 20 blade of the type illustrated in Figure 4,'

Figure 6 is a fragmentary sectional view taken along lines VI-VI of Figure 5, looking in direction'of arrows, and. I

Figure 7 is a fragmentary view showing an 25 application of the invention to the contacting parts of a bus bar system.

. Reference is now made toFigure 1 of the'drawing, wherein, for the purpose of thisdescription,

the invention is shown as applie'd'to a switch 30 blade and the cooperating clips of an air break switch of the so-called disconnecting" type.. -As

.here shown, the numeral Ill designates a switch clips which. are mounted upon a supporting member l4 carried at theen'dipf a second current conductin switchfarm IS; The switch 'arms I2 4 and i5 are pivoted at their outer ends so that the switch blade Ill {and the bladeengagiingcIips l3 move into, engagement along arcs of circles determined by the len'gthoi the switch arms 12 and I5;

As is better shown'in Figure 2 or the drawing, the switch clip supporting member l4 has op sitelydisposed side members that form box-like enclosures for the opposed contact clips" l3; and between whichthe Switchblade I!) may freely move into engagement between'the'blad'e engaging clips 13. These side members, designated by the numeral I6; are also shown as having blade guiding extensions I 11: -Theblade engaging clips l3 are yieldingly supported within the box-like members l6 by means of pressure exerting springs I8 in a conventional manner, and extending from the back of each of the clips l3 there is aflexible current conducting pigtail I 9 which serves to .conduct the current from the clips l3 to their supporting member H and to the current conducting switch arm l5.

Asshown in Figure 3 of the drawing, each of the contact clips I3 has a pair of longitudinally extending raised contact forming surfaces 20 which are preferably of silver, and as shown in Figure 4 of the drawing, the switch blade I0 is shown as having spaced longitudinally extending raised contact forming members 2| extending longitudinally along each side thereof. The contact forming members 20 upon the clips l3 and the members 2| upon the switch blade II are preferably formed by securing an outwardly projecting strip of silver upon the surface of the clips and blade in a novel manner to be now described.

The method of applying the contact forming members 20 to the clips l3 and the contact form--" ing members 2| to the switch blade I0 is clearly illustrated in Figures 5 and 6 of the drawing. As here shown, the switch blade I0 is provided with spaced and oppositely disposed grooves 22 into which a strip of silver or other non-insulating film forming metal 23 may be disposed. The grooves 22 may be straight-sided or undercut and are of a depth less than the thickness of the metal strip 23, so that the strips 23 will extend above the surfaces of the blade l0. When the blade has been grooved as above, a strip of the contact forming metal 23 having a proper contour and thickness is laid into one of the grooves 22 and then by the application of pressure through a roller or other tool 24 the metal 23 is pressed with a metal flowing pressure into intimate contact with the sides and bottom of the grooves 22, and at the same time the sides of the grooves 22 are rolled inwardly and into firm overlapping engagement with the sides of the contact forming strip 23. In this operation, asis better illustrated in Figure 6 of the drawing, the contact surface forming:- strip 23 is slightly deformed by the roller 24, and the metal thereof is caused to flow cold into intimate air excluding contact with'the bottom and sides of the grooves 22, while at the same time the inrolled sides of the groove 22 will firmly hold the metal strip 23 in this condition with its outer surface extending above the adjacent surfaces of the blade III.

The application of the contact forming member 20 to the clips I3 is carried out in a manner similar to that above described in connection with the formation of the switch blade l0. However, as shown in Figure 3 of. the drawing, the

grooves for the metal strips 20 do not extend around the curved ends of the clips l3, and therefore the contact forming members 20 are finished with a rounded end as at 25, to facilitate movement of the contact forming members 2| thereover, when the switch blade I moves into its circuit closing position between the clips l3.

While the invention has been described above as'applied to an air break, switch, it is to be understood that the invention is equally applicable to switches having oil immersed contacts.

In Figure '7 of the drawing, there is illustrated another use to which the invention is applicable. As here shown, the invention is applied to a bus bar system by securing contact forming strips 26 of silver, in the manner above described, upon a bus bar connection 21 which engages a bus bar 28. As here shown, the bus bar connection 21 is secured with the contact forming members 26 in high pressure engagement with the bus 28 by means of conventional triangular clamping plates 29 and bolts 30, in accordance with standard practice.

While silver has been above referred to as the preferred metal for the contact forming strips 20 and 2|, it is to be understood that this term is to include alloys of silver and other low resistance metals having the desired characteristics of silver. It is to be also understood that the contact forming strips 20 and 2| need not initially have a half-round configuration, as it is conceivable that -metal strips having other configurations may be rolled and pressed into the grooves 22 to produce a contact surface in accordance with the invention.

In conclusion it may be added that a halfround sterling silver strip of 986 fineness, having nating current with a constant 30 rise, which is within the permissible limit under A.- I. E. E. standards.

While I have, for the sake of cleamess and in order to disclose the invention so that the same can be readily understood, described and illustrated a specific arrangement, I desire to have it understood that this invention is not limited to the specific means disclosed, but may be embodied in other ways that will suggest themselves to persons skilled in the art. One such variation is that when the groove 22 is undercut as suggested, the sides of the groove need not be rolled in, as the silver, under this condition, will be flowed bypressure under the overhanging sides of the groove. It is-believed that this invention is new and it is desired to claim it so that all such changes as come within the scope of the appended claims are to be considered as part of this invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is- 1. In an electrical switch of the knife blade type, the combination of a blade-like member having longitudinally extending and oppositely disposed non-oxidizing contact surface forming members secured upon each side thereof, and cooperating blade engaging clips between which said blade-like member is adapted to move having transversely extending non-oxidizing contact surface forming members secured upon the blade engaging sides thereof, the contact surface forming members upon said blade-like member and the contact surface forming members upon said clips being half round in cross section and secontact forming members of a non-insulating 7s aioasaa film forming metal inlaid on the surfaces thereof, the raised non-insulating film forming members upon said blade-like member and upon said clips being half round in cross section and arranged to normally extend transverse to each other with their rounded sides engaging when the blade-like member is in its circuit closing position between the cooperating blade engaging clips.

3. In an electrical switch of the knife blade type, the combination of a blade-like member having parallel extending and oppositely disposed contact surface forming members of silver secured thereupon, and cooperating blade engaging clips between which said blade is adapted to move also having spaced contact surface forming members of silver secured upon the blade engaging sides thereof, said silver contact surface forming members upon said blade-like member and upon said cooperating blade engaging clips being half round in cross section and arranged to normally extend transverse to each other with their rounded surfaces engaging when the switch blade is in its circuit closing position between said clips.

4. In a circuit interrupter, the combination of a blade-like member of copper having a raised longitudinally extending contact forming surface of silver, said surface of silver being formed by grooving the surface of said blade and cold rolling a silver strip into said groove under pressure, a pair of full floating and opposed switch blade engaging clips also having a raised contacting surface of silver, extending longitudinally thereof and normally transverse to the raised silver surface upon said blade when the circuit interrupter is closed, the raised silver surface upon said opposed clips being also formed by cold rolling a strip of silver under pressure into a groove in the surface of said clips, and pressure producing means cooperating with said clips to produce a uniform contact pressure between the transversely disposed silver contact surfaces upon said blade and clips.

5. An improved contact surface construction for electrical apparatus comprising cooperating copper conductors each having spaced parallel and raised silver surfaces formed by cold pressing a strip of silver into grooves cut in the adjacent sides thereof, the disposition of said raised contact surfaces upon said current conducting members being such that when said members are connected together in current conducting relation said silver contact surfaces upon the respectiveconductors will lie transverse to each other.

6. An improved blade for electrical circuit interrupters comprising a blade-like member constructed of copper having a plurality of longitudinally extending grooves cut in the opposite sides thereof, and having raised silver contact making surfaces formed by cold flowing a strip of silver into intimate engagement with the bottom'and sides of said grooves. 4

7. In a contact engaging clip for an electrical switch, the combination of a pair of oppositely disposed contact forming members having raised silver contact surfaces extending in the line of movement of the cooperating contact, said raised silver contact surfaces being formed by cold pressing a strip of silverinto a groove cut in the face of said contact members, and a pressure producing means disposed in cooperating relation with said contact members to produce a high contact pressure between said silver contact surfaces and a cooperating circuit completing member of the switch.

ROY WILKINS. 

